Refractory metal silicide target, method of manufacturing the target, refractory metal silicide thin film, and semiconductor device

ABSTRACT

A refractory metal silicide target is characterized by comprising a fine mixed structure composed of MSi 2  (where M: refractory metal) grains and Si grains, wherein the number of MSi 2  grains independently existing in a cross section of 0.01 mm 2  of the mixed structure is not greater than 15, the MSi 2  grains have an average grain size not greater than 10 μm, whereas free Si grains existing in gaps of the MSi 2  grains have a maximum grain size not greater than 20 μm. The target has a high density, high purity fine mixed structure with a uniform composition and contains a small amount of impurities such as oxygen etc. The employment of the target can reduce particles produced in sputtering, the change of a film resistance in a wafer and the impurities in a film and improve yield and reliability when semiconductors are manufactured.

This application is a continuation of application Ser. No. 08/397,243filed on Mar. 20, 1995, now U.S. Pat. No. 6,309,593 B1 which wasoriginally filed as PCT/JP94/01236 on Jul. 27, 1994.

TECHNICAL FIELD

The present invention relates to a refractory metal silicide target, amethod of manufacturing the target, a refractory metal silicide thinfilm, and a semiconductor device, and more specifically, to a refractorymetal silicide target, a method of simply manufacturing the target, arefractory metal silicide thin film, and a semiconductor device capableof reducing the generation of particles in sputtering and forming a thinfilm of high quality by densifying or fining a mixed structure andmaking a uniform composition and further achieving high density and highpurification.

BACKGROUND ART

A sputtering method is employed as one of the effective methods offorming a refractory metal silicide thin film used for a gate electrode,source electrode, drain electrode of semiconductor devices such as MOS,LSI devices and the like and for wiring. The sputtering method, which isexcellent in mass-productivity and the stability of a formed film, is amethod such that argon ions are caused to collide with a disc-shapedrefractory metal silicide target and discharge a target constitutingmetal which is deposited as a thin film on a substrate disposed inconfrontation with the target. Consequently, the property of thesilicide thin film formed by sputtering greatly depends upon thecharacteristics of the target.

Recently, as a semiconductor device is highly integrated andminiaturized, it is required that a sputtering target used to form arefractory metal silicide thin film produces a less amount of particles(fine grains). That is, since particles produced from a target duringsputtering have a very fine grain size of about 0.1-10 μm, when theparticles are mixed into a thin film being deposited, they cause aserious problem that the yield of semiconductor devices is greatlyreduced by the occurrence of short circuit between wires of a circuitand insufficient opening of wires. Thus, the reduction of an amount ofparticles is strongly required.

Since it can become effective means to miniaturize a target structure,that is, to make the size of MSi₂ grains and free Si grains as small aspossible in order to reduce an amount of particles produced from atarget, there are conventionally proposed various manufacturing methodsof miniaturizing the structure.

For example, Japanese Patent Application Laid-Open No. Sho63(1988)-219580 discloses that a high density target having a finestructure and containing a small amount of oxygen can be obtained insuch a manner that a mixed powder obtained by mixing a high purityrefractory metal powder with a high purity silicon powder is subjectedto a silicide reaction in high vacuum and a semi-sintered body isformed, then the resultant semi-sintered body is charged into apressure-tight sealing canister without being crushed and thepressure-tight sealing canister is sintered by a hot isostatic pressafter having evacuated and sealed. In this case, the thus obtainedtarget has a fine structure having the maximum grain size of MSi₂ notgreater than 20 μm and the maximum grain size of free Si not greaterthan 50 μm and containing oxygen not greater than 200 ppm with a densityratio not less than 99%.

Further, Japanese Patent Application Laid-Open No. Hei 2(1990)-47261discloses that a high density target with a fine structure can beobtained in such a manner that a mixed powder of a high purityrefractory metal powder and a high purity silicon powder is subjected toa silicide reaction in high vacuum and a semi-sintered body is formed,then the semi-sintered body is crushed to not greater than 150 μm andfurther added and mixed with a high purity silicon powder and chargedinto a pressure-tight sealing canister, then the pressure-tight sealingcanister is sintered by a hot isostatic press after having evacuated andsealed. In this case, the thus obtained target has a maximum grain sizeof MSi₂ not greater than 20 μm and a density ratio not less than 99%with only free Si existing in a grain boundary.

Recently, as a semiconductor device is highly integrated andminiaturized, a high purity target containing a very small amount ofimpurities, which deteriorate the characteristics of the semiconductordevice, is required as a sputtering target used to form a refractorymetal silicide thin film. In particular, it is strongly required tominimize an amount of oxygen in a target because oxygen, whichconcentrates on the interface between a silicide layer and an underlayer and increases a film resistance, delays signals and lowers thereliability of the device.

Since it is effective oxygen reducing means to make deoxidation byheating a semi-sintered body as a material in vacuum and volatilizingoxygen in the form of silicon oxide (SiO or SiO₂), the followingmanufacturing methods of reducing oxygen are conventionally proposed.

For example, Japanese Patent Application Laid-Open No. Sho62(1987)-171911 obtains Mo silicide or W silicide each containing asmall amount of oxygen in such a manner that a mixed powder obtained bymixing a Mo powder or W powder with a Si powder is heated in vacuum at atemperature less than 800-1300° C. and a Mo silicide powder or Wsilicide powder is synthesized, then the resultant powder is held invacuum at 1300-1500° C. to remove oxygen as SiO by excessive Si.

On the other hand, a trial for optimizing the grain size of a materialpowder and hot pressing conditions from a view point that thecondensation of free Si results to an increase of particles produced andthe following manufacturing method is proposed.

For example, Japanese Patent Application Laid-Open No. Sho63(1988)-74967 obtains a target from which condensed silicon is removedin such a manner that a mixed powder obtained by adding a synthesizedsilicide powder of −100 mesh with a silicon powder of −42 mesh is heatedto 1300-1400° C. while applying a preload of 60-170 kg/cm², then pressedwith a pressing pressure of 200-400 kg/cm² and held after being pressed.

Further, Japanese Patent Application Laid-Open No. Sho 64(1989)-39374obtains a target from which condensed silicon is removed in such amanner that two types of synthesized silicide powders of −100 meshhaving a different composition are prepared and a mixed powder adjustedto have an intended composition is hot pressed under the same conditionsas above.

There is a problem, however, that when all the amounts of a mixed powdernecessary to form a single target is subjected to a silicide synthesisat once in high vacuum in the above conventional manufacturing methods,resulting MSi₂ grains are rapidly grown and coarsened as well as cracksare made to an entire semi-sintered body by a rapidly increasedtemperature in a silicide reaction because the silicide reaction is anexothermic reaction, and when the semi-sintered body is sintered bypressing in the state as it is, a resultant sintered body cannot be usedbecause the cracks remain.

There is also a problem that since a mixed material powder overflowsfrom a vessel by the rapid increase of temperature in the silicidereaction and a composition is out of an intended composition due to thevolatilization of very volatile Si. Thus, when the semi-sintered body issintered by pressing in the state as it is, a target having a desiredcomposition cannot be obtained.

Further, there is a problem that even if a semi-sintered body is crushedand made to a powder, since hard MSi₂ particles which have been grownonce and coarsened remain without being finely crushed, a target havinga uniform and fine structure cannot be obtained as well as an amount ofcontamination caused by impurities is increased by crushing and inparticular an amount of oxygen is greatly increased.

On the other hand, as disclosed in Japanese Patent Application Laid-OpenNo. Sho 62(1987)-171911, when a mixed powder is subjected to a silicidesynthesization at 800-1300° C. and further deoxidized by being heated tohigh temperature so as to reduce impurity oxygen, there is a problemthat since the sintering property of a resultant semi-sintered body isexcessively improved, the semi-sintered body cannot be sufficientlycrushed in a subsequent crushing process and formed to a segregatedstructure in which MSi₂ and Si are irregularly dispersed, and inparticular, when a heating temperature reaches a temperature regionexceeding 1400° C., this tendency is made more remarkable.

Although a semi-sintered body is crushed in an atmosphere replaced withAr (argon gas) to prevent an increase of an oxygen content, it isdifficult to completely prevent the contamination by oxygen when thesemi-sintered body is crushed. Further, a problem also arises in thatwhen a crushed powder is taken out from a vessel such as a ball mill orthe like, the powder surely adsorbs oxygen to increase oxygen containedtherein, and as a result a finely crushed powder has an increasedsurface area and an amount of oxygen adsorbed by the powder is greatlyincreased.

On the other hand, even if a synthesized powder was hot pressed whileapplying a preload of 60-170 kg/cm² thereto according to the methods ofJapanese Patent Application Laid-Open No. Sho 63(1988)-74967 andJapanese Patent Application Laid-Open No. Sho 64(1989)-39374, condensedsilicon was disadvantageously produced and a target having a fine anduniform structure could not be obtained.

Further, when a synthesized powder was hot pressed without being appliedwith a preload, MSi₂ grains obtained by synthesization was grown as wellas a composition has an inclined distribution in a target and it wasdifficult to obtain a target having a fine and uniform structure.

Japanese Patent Application Laid-Open No. Sho 62(1987)-70270 discloses arefractory metal silicide target having a density ratio not less than97%. Further, Japanese Patent Application Laid-Open No. Sho62(1987)-230676 discloses a methods of manufacturing a refractory metalsilicide target and describes that a target is molded by compactingusing a single axis under the conditions of high temperature, highvacuum and high pressing pressure.

However, the above respective prior arts describe only that a target ismade by subjecting a material powder for the target to hot pressing andno description is made as to a fine and uniform structure. Thus, theseprior arts cannot achieve an object for effectively suppressingparticles.

On the other hand, International Patent Application published accordingto PCT (No. WO91/18125 discloses a silicide target having 400×10⁴ piecesof silicide with a grain size of 0.5-30 μm existing in a cross sectionof the mixed structure of the target of 1 mm² with the maximum grainsize of Si not greater than 30 μm and further a silicide target with theaverage grain size of silicide of 2-15 μm and the average grain size ofSi of 2-10 μm.

Since the manufacturing method described in the prior art isinsufficient to obtain a fine uniform target structure, the object tosuppress the occurrence of particles cannot be sufficiently achieved.

An object of the present invention is to provide a high density andpurity refractory metal silicide target which has a fine mixed structureand a uniform composition as well as contains a less amount ofimpurities such as oxygen and the like, a method of manufacturing thetarget, a refractory metal silicide thin film and a semiconductordevice.

DISCLOSURE OF THE INVENTION

As a result of a zealous study why particles are generated, theinventors of this invention have obtained the following knowledge forthe first time:

(1) since free Si has a sputtering rate larger than that of MSi₂, assputtering proceeds, MSi₂ is exposed on an erosion surface and MSi₂grains having a weak bonding force with adjacent grains are liable to beremoved from the erosion surface, and in particular very fine MSi₂grains remarkably exhibit this tendency;

(2) although the form of erosion in a free Si portion exhibits awave-shape, as the Si portion increases, the distal end of thewave-shape is made acute and further the height of the wave-shapeincreases, thus the distal end of Si is dropped off or lacked by thethermal fluctuation in sputtering so that Si is liable to becomeparticles; and

(3) when pores remain in the interface between MSi₂ and free Si of atarget or in the interior of free Si, projections are formed around thepores, and abnormal electric discharge occurs in the portion where theprojections exist in sputtering, by which the projections are dropped orlacked and made to particles, and the like.

Further, the inventors have found it is very effective to suppress thegeneration of the particles that:

(1) a fine mixed structure is formed such that the number of MSi₂ grains(M: refractory metal) which independently exist on any arbitrary surfaceor in a cross section of 0.01 mm² of the mixed structure is not greaterthan 15, MSi₂ has an average grain size not greater than 10 μm and freeSi existing in the gaps of MSi₂ has a maximum grain size not greaterthan 20 μm;

(2) the mixed structure is arranged such that a Si/M atom ratio X in 1mm² of the mixed structure has a dispersion of X±0.02 and free Si isuniformly dispersed; and

(3) a density ratio is not less than 99.5% over the entire surface of atarget, and the like.

Further, the inventors have found that the growth of MSi₂ grainsproduced can be suppressed and a large dislocation (dispersion of acomposition ratio) of a composition can be prevented withoutvolatilizing almost all the Si in such a manner that when silicide issynthesized once in a silicide synthesizing process, mixed powders eachdivided to a small amount of lot are charged into a compacting mold,that is, a depth of the compacting mold to which the mixed powders arecharged is set to not deeper than 20 mm and the mixed powders are heatedin vacuum and synthesized.

Further, to reduce impurities in a target and increase its purity, theinventors have found that:

(1) a refractory metal silicide semi-sintered body containing a lessamount of oxygen not greater than 200 ppm which cannot be obtained byprior art can be obtained in such a manner that a semi-sintered bodyobtained by synthesizing silicide is crushed once and a resultantcrushed powder is deoxidized by being heated in vacuum or in apressure-reduced hydrogen atmosphere in stead of deoxidizing thesemi-sintered body by heating it in the state as it is;

(2) when a plurality of powder charging vessels each having the sameinside diameter are prepared and crushed powders are deoxidized so thatsemi-sintered bodies can be sintered in a shape as they are by a hotisostatic press method or the like, since the semi-sintered bodies havethe same shape, a plurality of semi-sintered bodies can be sintered atthe same time and there is an advantage that the productivity of targetscan be improved;

(3) when the silicide synthesis is performed in a vacuum furnace using agraphite heater and insulator, a semi-sintered body obtained by thesynthesization is mixed with carbon and iron and contaminated by them.In contrast, when the silicide synthesis is performed in a vacuumfurnace using a heater and an insulator each composed of a high purityrefractory material, the contamination can be effectively prevented; and

(4) contamination caused by impurities contained in a material can beeffectively prevented by crushing a semi-sintered body in a ball millhaving a ball mill main body the inside of which is lined with a highpurity material and crushing mediums (balls) formed of a high puritymaterial, and the like.

Further, as a result of a zealous study of hot pressing conditionseffected by using a synthesized powder, the inventors have found thatthe size of MSi₂ grains produced is different depending upon atemperature for applying a pressing pressure and how the temperature isincreased and that the composition in a target has an inclineddistribution in accordance with the temperature and pressure conditions.More specifically, the inventors have found that when a synthesizedpowder is heated up to just below an eutectic temperature and thenapplied with a pressing pressure, MSi₂ grains formed by synthesizationare regrown and that free Si flows in the direction of the end of atarget and its composition has an inclined irregular distribution as theMSi₂ grains grow.

Further, the inventors have obtained the knowledge that when a certaindegree of a pressing pressure is applied at a temperature step less than1200° C. and then heating is effected stepwise or at a low rate up tojust below an eutectic temperature and further a larger pressingpressure is applied, the growth of MSi₂ grains is effectively prevented,the composition in a target is made uniform and a density of the targetis increased for the first time.

The present invention has been completed based on the above knowledges.

More specifically, a refractory metal silicide target according to thepresent invention is characterized by comprising a fine mixed structurecomposed of MSi₂ (where M: refractory metal) grains and Si grains,wherein the number of MSi₂ grains independently existing in a crosssection of 0.01 mm² of the mixed structure is not greater than 15, theMSi₂ grains has an average grain size not greater than 10 μm, whereasfree Si grains existing in the gaps of the MSi₂ grains have a maximumgrain size not greater than 20 μm. Specifically, W, Mo, Ti, Ta, Zr, Hf,Nb, V, Co, Cr, Ni are used as the metal (M) constituting the above metalsilicide (MSi₂).

Note, the shape and the number of MSi₂ grains and Si grains in the abovemixed structure are measured as follows. That is, the maximum grainsize, average grain size and number of MSi₂ grains are measured in sucha manner that a photograph showing the structure of a target sinteredbody is obtained by photographing a fracture surface of the sinteredbody under a scanning type electron microscope (SEM) at a magnificationratio of 1000 and thus obtained photograph is then analyzed with animage analyzer. A visual field to be image-analyzed must cover 10points.

On the other hand, the maximum grain size, average grain size and numberof free Si grains and chain-shaped (link-formed) Si grains are measuredin such a manner that a photograph showing the structure of a targetsintered body is obtained by photographing a polished surface of thesintered body under a scanning type electron microscope (SEM) at amagnification ratio of 1000, then the photograph is analyzed with animage analyzer. In that case, 5 cross sections obtained by equallydividing the polished surface in the thickness direction thereof at apitch of 10 μm were measured and when Si grains are freed from other Sigrains, they are regarded as free Si, whereas when Si grains are coupledwith other Si grains at any portion thereof, they are regarded aschain-shaped Si. A visual field must cover 20 points in each crosssection.

Since Si is more deeply eroded than MSi₂ by sputtering in the abovemixed structure, preferable is a structure arranged such that MSi₂grains are coupled each other like a chain and Si grains exist in thegaps of the MSi₂ grains to reduce particles generated in a targetbecause MSi₂ grains are liable to be removed or dropped from an erodedsurface in a portion where MSi₂ independently exists in Si phase.

When the size of MSi₂ grains is increased, Si is selectively scatteredfrom MSi₂ and forms projections like grains. Since these projections arereleased and made to particles, the average grain size of MSi₂ ispreferably not greater then 10 μm and more preferably not greater than 5μm to prevent the occurrence of the projections. On the other hand, Siis eroded to a wave-shape by sputtering, and as the size of Si isincreased, the wave-shape is made acute and deep and Si is liable to belacked or dropped off. Thus, the maximum grain size of Si is preferablynot greater than 20 μm, more preferably not greater than 15 μm, andfurther more preferably not greater than 10 μm.

When the average value of a Si/M atom ratio in an entire target isassumed to be X, it is preferable that the dispersion of the Si/M atomratio in an arbitrary cross section of 1 mm² in the mixed structure ispreferably set within the range of X±0.02. That is, when MSi₂ and Siirregularly disperse even if a target has a fine structure, inparticular when free Si is locally concentrated and irregularlydistributed, since the structure in the target is greatly changed aswell as a plasma electric discharge is unstably carried out andparticles are induced, the dispersion of the Si/M atom ratio X in anarea of 1 mm² is preferably X±0.02 and more preferably X±0.01.

It is preferable to form a high density silicide target in which thedensity ratio of a target is not less than 99.5% over the entire target.When there remain many pores (holes) due to an insufficient density of atarget, the pores exist in an interface between MSi₂ and Si or in theinterior of Si, projections are formed around the pores in sputtering,an abnormal electric discharge is caused in the portion of theprojections and the projections are broken and released by thedischarge, which results in the occurrence of particles. Thus, the poresmust be reduced as few as possible, and for this purpose, the densityratio of target is preferably not less than 99.5%, more preferably notless than 99.7% and further more preferably not less than 99.8% over theentire target.

It is preferable that a content of oxygen as an impurity is set to notgreater than 200 ppm and a content of carbon as an impurity is set tonot greater than 50 ppm. When oxygen is taken into a deposited thin filmby sputtering a target containing oxygen, silicon oxide is formed in theinterface of the thin film and a resistance of the film is increased bythe silicon oxide. Thus, to further reduce the resistance of the film,an oxygen content in target is preferably set to not greater than 200ppm and more preferably not greater than 100 ppm. Further, since carbonalso increases a resistance of the film by forming silicon carbide, acarbon content in target is preferably set to not greater than 50 ppmand more preferably not greater than 30 ppm to reduce the resistance ofthe film.

The contents of iron and aluminium as impurities are set to not greaterthan 1 ppm, respectively. When iron and aluminium are mixed into adeposited thin film, a deep level is formed in the interface of the thinfilm and causes a leakage in connection, by which a semiconductor ispoorly operated and its characteristics are deteriorated. Thus, an ironcontent and aluminium content in target are preferably set to notgreater than 1 ppm, respectively and more preferably not greater than0.5 ppm, respectively.

Next, a method of manufacturing a refractory metal silicide targetaccording to the present invention will be described below.

In a process I (step I), a refractory metal powder having a maximumgrain size not greater than 15 μm is blended with a silicon powderhaving a maximum grain size not greater than 30 μm such that a Si/M atomratio (value X in MSi_(x)) is 2-4 and these powders are sufficientlymixed each other in a dry state using a ball mill, V-type mixer or thelike so that the silicon powder uniformly disperses in the refractorymetal powder. The irregularly mixing of them is not preferable becausethe structure and composition of a target is made irregular andcharacteristics of the film formed by using the target are deteriorated.The powders are preferably mixed in a vacuum of not higher than 1×10⁻³Torr or in an inert gas atmosphere such as an argon gas to preventcontamination by oxygen. In particular, when a pulverizer or powdercrushing mixer such as a ball mill or the like is used, contamination byimpurities can be effectively prevented by performing mixing operationin a dry state using a ball mill having a main body the inside of whichis lined with a high purity material not less than 5N (99.999%) andcrushing mediums (balls) composed of a high purity material so thatcontamination caused by impurities from a crusher main body can beprevented.

The same material as the refractory metal (M) constituting a target ispreferably used as the above high purity material and, for example, W,Mo, Ti, Ta, Zr, Hf, Nb, V, Co, Cr, Ni etc. are used.

As a method of lining the pulverizer main body with the high puritymaterial, there can be employed a method of lining a high puritymaterial sheet, a method of integrally forming a high purity materiallayer on the inner surface of a main body by various depositing methodssuch as CVD, plasma vapor deposition, and the like.

The refractory metal powder and silicon powder used as a target materialpreferably contain impurities, which deteriorate characteristics of asemiconductor device, in an amount as small as possible and preferablyhave a purity not lower than 5N (99.999%). Further, since coarse powderscoarsen formed MSi₂ grains and si grains and lowers the dispersingproperty of Si, the refractory metal powder preferably has a gain sizenot greater than 15 μm and the silicon powder preferably has a grainsize not greater than 30 μm. Further, the refractory metal powderpreferably has a grain size not greater than 10 μm and the siliconpowder preferably has a grain size not greater than 20 μm. Furthermore,the refractory metal powder preferably has a gain size not greater than5 μm and the silicon powder preferably has a grain size not greater than10 μm.

A reason why the value X of the Si/M atom ratio is limited to 2≦X≦4 isas described below. That is, when the value X is less than 2, free Sireduces and further disappear in a silicide target and the structuredefined by the present invention cannot be obtained. On the other hand,when the value X exceeds 4, since free Si continuously exists, there isobtained a structure in which MSi₂ grains exist in a Si matrix.Consequently, the structure of the present invention that MSi₂ grainsare coupled each other like a chain and Si grains exist in the gaps ofthe MSi₂ grains is difficult to be obtained. Further, when the value Xis less than 2, since a large tensile strength is produced in a formedsilicide film, the close contact property of the film with a substrateis deteriorated and the film is liable to be exfoliated or peeled fromthe substrate. On the other hand, when the value X exceeds 4, since afilm resistance increases, a resultant film is improper as an electrodewiring film. Further, when a mixed powder having the value X not lessthan 2 is synthesized to silicide, since free Si exists, there is anadvantage that a crushing property is improved in a process III to bedescribed below.

Si is preferably blended in an amount which is a little in excess of theamount of an intended composition by taking an loss caused by thevolatilization of a Si and SiO₂ film covering the surface of Si powdersinto account.

A process II is a process for synthesizing refractory metal silicide aswell as forming a semi-sintered body by charging the mixed powderprepared in the process I into a compacting mold and heating the powderin high vacuum or in an inert gas atmosphere. In the process II, sincean amount of the mixed powder to be charged into the compacting mold andsubjected to a synthesizing operation effected once affects the size ofMSi₂ grains to be produced and an amount of Si to be volatilized, it ispreferable to set an amount of the mixed powder charged once to a depthnot higher than 20 mm. When the depth of charge exceeds 20 mm, formedMSi₂ grains are coarsened due to a temperature increase caused by asilicide reaction and the powder may be caused to overflow from thevessel by an explosive reaction. On the other hand, when the mixedpowder to be charged into the vessel has a depth not higher than 1 mm,the number of vessels used for a single target is greatly increased aswell as an amount of production per a synthesizing treatment is greatlyreduced, and productivity is lowered. Thus, a preferable depth of chargeis 1-10 mm. When Mo is used as a refractory metal powder, however, anamount of the mixed powder to be charged into a vessel is preferably setto a depth not higher than 10 mm and more preferably a depth not higherthan 5 mm because a particularly high calorific value is generated by asilicide reaction.

A vessel used here is preferably composed of a high purity Mo, W, Ta, Nbmaterial or the like to prevent the contamination of the mixed powdercaused by impurities generated from the vessel and thermal deformation.Further, it is preferable to use the same metal material as a refractorymetal (M) constituting intended refractory metal silicide. Further, theflat portion of the vessel may be set to such a shape and size as toenable the vessel to be inserted into calcining equipment such assintering furnace.

As a heating pattern, it is preferable to effect heating stepwise from atemperature 200° C. lower than a silicide reaction start temperature tosuppress the growth of MSi₂ grains and minimize the change of acomposition. A temperature increasing width is preferably 20-200° C.That is, when the temperature increasing width is less than 20° C., along time is needed to synthesization and productivity is lowered,whereas the width exceeds 200° C. MSi₂ grains are grown and the powderis caused to overflow from the vessel by an abrupt increase oftemperature, and a composition is changed and the interior of thefurnace is contaminated. Further, each temperature is preferably heldfor 0.1-3 hours. When the holding time is less than 0.1 hour, thetemperature of the powder in the vessel is not made uniform and atemperature difference abruptly increases, and MSi₂ grains arecoarsened. On the other hand, when the holding time exceeds 3 hours, along time is needed for synthesization and productivity is lowered.Note, the temperature increasing width is preferably set to 20-200° C.and more preferably to 50-100° C. and the holding time is morepreferably set to the range of 0.5-2 hours. In particular, when thetemperature is increased to a temperature of 100° C. or more higher thanthe silicide reaction start temperature, it is preferable to set a longholding time at the silicide reaction start temperature or within thestart temperature +50° C. and the holding time is preferably not shorterthan 1 hour. The silicide reaction start temperature can be determinedby detecting when a degree of vacuum in the furnace is lowered by thevolatilization of Si or silicon oxide (SiO or SiO₂) caused by a reactionheat.

Further, the same effect can be achieved by carrying out heatingoperation slowly in place of the stepwise heating. In this case, aheating rate is preferably controlled to 5° C./minute or less. When theheating rate is excessively large, MSi₂ grains are grown as well as thepowder is caused to overflow from the vessel, the composition is changedand the interior of a furnace is contaminated by the abrupt increase ofthe temperature.

A maximum heating temperature in synthesization is preferably increasedup to 1100° C. so that a silicide reaction starts and synthesization iscompleted. Since a reaction temperature is different depending upon anamount of oxygen contained in the mixed powder, however, the maximumheating temperature is preferably increased to about 1300° C. by takingthe reduction of the oxygen content into consideration. When thetemperature is increased to higher than 1300° C., the sintering of asemi-sintered body formed by a silicide reaction proceeds and itscrushing in a process III is made difficult and further free Si ismelted as well as MSi₂ grains are grown and coarsened by an eutecticreaction. Thus, there is obtained a structure in which MSi₂ grains andSi grains irregularly disperse and as a result a silicide target havingan intended crystal structure cannot be obtained. On the other hand,when the maximum heating temperature is not higher than 1000° C., thesilicide reaction does not start and synthesization is made impossibleexcept the case that M is Ni. Thus, a more preferable temperature rangeis 1150-1250° C.

Note, when the above maximum heating temperature is excessively high inthe case M is Ni, sintering is liable to proceed as compared with thecase M is other than Ni. Thus, the temperature is preferably increasedup to about 800° C. and more preferably in the range of 700-800° C. onlywhen Ni is used.

When a refractory metal silicide is synthesized as well as asemi-sintered body is formed in the process II, a vacuum furnaceemployed for heating is preferably, for example, a vacuum furnace usinga high purity Mo heater or a high purity W heater and an insulatorcomposed of a high purity refractory material, by which a semi-sinteredbody obtained by synthesization can be effectively protected fromcontamination caused by impurities from the heater and insulator.

In a process III, a refractory metal silicide semi-sintered body whichis obtained by synthesizing silicide and has an atom ratio X of 2≦X≦4,is crushed or pulverized and a crushed powder is prepared. A powder lumpin which free Si segregated to an aggregation of MSi₂ formed insynthesization exists is finely crushed and uniformly dispersed by thecrushing process. When this dispersing operation is no effecteduniformly, since the dispersion of MSi₂ and free Si is lowered, thestructure and composition of a target are not uniformly arranged and afilm characteristics are deteriorated, a crushing time is preferably notshorter than 24 hours. On the other hand, although the longer thecrushing time, the more improved is a crushing efficiency, sinceproductivity is lowered and an amount of contamination is increased byoxygen, the crushing time is preferably not longer than 72 hours. Themaximum grain size of a powder obtained by the crashing is an importantfactor for obtaining a fine uniform structure defined by the presentinvention. Therefore, the maximum grain size is preferably not greaterthan 20 μm and more preferably not greater than 15 μm in order to obtainthe structure defined by the present invention that MSi₂ grains have anaverage grain size not greater than 10 m and free Si grains have amaximum grain size not greater than 20 μm.

The crushing is preferably effected in vacuum or in an inert gasatmosphere similarly to the process I to prevent the contamination byoxygen. In particular, when a crushing mixer such as a ball mill or thelike is used, contamination by impurities can be effectively preventedby carrying out mixing operation in a dry state using a ball mill havinga main body the inside of which is lined with a high purity material andcrushing mediums (balls) composed of a high purity material so thatcontamination caused by impurities from the crusher main body can beprevented.

Further, it is preferable that the following impurity removing processis followed by the process III to remove impurities contained in thecrushed power such as oxygen, carbon etc. That is, the impurity removingprocess is a process for heating the crushed powder prepared in theprocess III and preparing a high purity powder and a high puritysemi-sintered body by removing impurities such as in particular oxygenand the like therefrom. A heating temperature is preferably set to1150-1300° C. to effectively remove oxygen adsorbed to the crushedpower. More specifically, when the heating temperature is less than1150° C., it is difficult to obtain a low oxygen target containingoxygen in a amount not greater than 200 ppm by volatilizing and removingoxygen as silicon oxide (SiO or SiO₂). On the other hand, when theheating temperature exceeds 1300° C., a problem arises in that free Siis greatly volatilized and lost, and it is difficult to obtain a targethaving a predetermined composition, and further a semi-sintered body iscracked, sintering proceeds and an amount of contraction increases, andthe semi-sintered body cannot be hot pressed in the state as it is.Consequently, a more preferable temperature range is 1200-1250° C.

In particular, when the heating temperature increases, since thesemi-sintered body is liable to be cracked, it is preferable that thesemi-sintered body is processed while applying a low pressing pressurethereto. The pressure is preferably in the range not greater than 10kg/cm².

Further, the above heating temperature is preferably held for 1-8 hours.When the holding time is shorter than 1 hour, oxygen is insufficientlyremoved, whereas when the time exceeds 8 hours, a long time is neededand productivity is lowered as well as a large amount of Si isvolatilized and lost, and the dislocation of the composition of asilicide target increases. Thus, the holding time is more preferably setto the range of 2-5 hours.

A degree of vacuum is preferably set to not higher than 10⁻³ Torr andfurther to not higher than 10⁻⁴ Torr to more effectively reduce oxygenby volatilizing silicon oxide. A further deoxidizing effect can beobtained and a target containing a less amount of oxygen can be obtainedin such a manner that after the degree of vacuum is adjusted, hydrogenis introduced into a heating furnace and the target is heated in apressure-reduced hydrogen atmosphere.

A vessel into which the crushed powder is charged may have a shape andsize equal to those of a compacting mold to be used in a sinteringprocess such as a hot pressing or the like to be described later or maybe formed to a size determined by taking an amount of contraction of asemi-sintered body caused by calcination into consideration. As aresult, there can be obtained an advantage that a deoxidizedsemi-sintered body can be easily inserted into the compacting mold and aplurality of semi-sintered bodies can be simultaneously sintered, andproductivity can be greatly improved. The vessel is preferably composedof a high purity material of Mo, W, Ta, Nb or the like to prevent thecontamination of the crushed powder by impurities and thermaldeformation.

The crushed powder charged into the vessel is preferably smoothed by adedicated pattern and made to flat by moving the powder forward andbackward and in rotation so that the deoxidized semi-sintered body canbe hot-pressed in the state as it is.

In a process IV, a crushed powder prepared in the process III or asemi-sintered body having been subjected to the impurity removingprocess is subjected to a main sintering and densification orcompaction. The crushed powder or semi-sintered body having beensubjected to the impurity removing process whose Si/M atomic ratio isadjusted to 2-4 and which is composed of MSi₂ and excessive Si ischarged into the compacting mold and sintered and densified whilesetting a temperature and pressure at two steps.

The compacting mold to be used here is preferably a graphite compactingmold arranged such that, for example, a BN powder or the like having anexfoliation resistance at high temperature is coated on the innersurface of the mold with a spray or brush as a mold releasing agent andfurther a partition plate is applied onto the inside surface through adouble-coated adhesive tape, adhesive or the like. The mold releasingagent is coated to prevent a compacting mold main body from being fusedto the partition plate in hot pressing. The partition plate is providedto prevent the direct contact of the semi-sintered body with the moldreleasing agent and isolate the former from the latter. As the partitionplate, a refractory metal such as Mo, W, Ta, Nb etc. enduring hightemperature in sintering and Ni, Ti etc. excellent in workability andprocessability is used by being formed to a thickness of 0.1-0.2 mm.When the partition plate is excessively thick, since its strength isincreased, the formability of the plate is lowered when it is appliedonto the compacting mold and workability is lowered as well as since thepartition plate is adhered onto a sintered body, a long time is neededto remove it by grinding or the like. On the other hand, when thepartition plate is too thin, since its strength is small, the plate isdifficult to handle and workability is also lowered.

The fusion of the compacting mold with the partition plate is preventedas well as the mold releasing agent is not exfoliated and removed andthe mixing of impurities contained in the mold releasing agent with asintered body can be effectively prevented by coating the mold releasingagent on the inner surface of the mold and further using the compactingmold on which the partition plate is applied. In particular, even if BNis used as the mold releasing agent, the contamination of a targetcaused by inevitably contained impurities such as aluminium, iron etc.can be effectively prevented.

Next, sintering is carried out by applying a low pressing pressure of10-50 kg/cm² in a high vacuum not higher than 10⁻³ Torr and increasing atemperature up to just below an eutectic temperature stepwise or at asmall temperature increasing rate.

A pressing pressure is preferably set to 10-50 kg/cm² at a first stepbecause the pressure affects the remaining of aggregated silicon and thegrain size of MSi₂. When the pressing pressure is less than 10 kg/cm²,MSi₂ grains grow as well as a composition is not uniformly distributed.On the other hand, when the pressure is not less than 50 kg/cm², theductile flow of free Si is suppressed and aggregated Si remains, and astructure in which Si is not uniformly dispersed is obtained. Thepressure is more preferably 20-30 kg/cm².

When sintering is carried out by increasing a temperature up to justbelow an eutectic temperature while applying a pressure, heating ispreferably effected stepwise or at a low temperature increasing rate tosuppress the growth of MSi₂ grains. A temperature increasing width ispreferably 20-200° C. When the temperature increasing width is less than20° C., a long time is needed for sintering and productivity is lowered,whereas when the width exceeds 200° C., MSi₂ grains are grown by anabrupt temperature increases as well as a composition has an inclineddistribution in a target plane due to the flow of free Si. Further, eachtemperature is preferably held for 0.1-3 hours. When the holding time isless than 0.5 hour, the temperature of a sintered body in a mold is notuniformly distributed, whereas when the time exceeds 2 hours, a longtime is needed and productivity is lowered. Thus, it is more preferablethat the temperature increasing width is set to the range of 50-100° C.and the holding time is set to the range of 0.5-2 hours.

Further, when a heating rate exceeds 20° C./minute in the heatingeffected at a low rate, MSi₂ grains are coarsened. Thus, the heatingrate is preferably set to not higher than 20° C./minute. Further, whenthe heating rate is less than 3° C./minute, since a long time is neededto sintering operation and productivity is lowered, it is preferably setto the range of 3-20° C./minute and more preferably to the range of5-10° C./minute.

A final sintering temperature T is preferably set to just below aneutectic temperature, i.e., to the range of Ts−50≦T<Ts. When, forexample, W, Mo, Ti, Ta are used as M, the eutectic temperature Ts is1400, 1410, 1330, 1385° C., respectively. Note, the eutectic temperatureTs can be easily obtained by referring to literatures such as“Constitution of Binary Alloys” (Dr. phil. Max Hansen and Dr. KurtAnderko; McGraw-Hill Book Company, 1958) and the like. When T is nothigher than (Ts−50), pores remain and a desired high density targetcannot be obtained, whereas when T is not less than Ts, free Si ismelted and flows out from the compacting mold and a target with adislocated composition is obtained.

Since a pressing pressure at a second step affects the density of aresultant sintered body, the pressure is preferably set to 200-500kg/cm². When the pressing pressure is less than 200 kg/cm², a sinteredbody with a density not less than 99% cannot be obtained, whereas whenthe pressure is not less than 500 kg/cm², a graphite compacting mold isliable to be broken. Thus, the pressing pressure is more preferably setto the range of 300-400 kg/cm².

The pressing pressure is preferably applied in 1-5 hours after a finaltemperature is reached. When the period of time is less than 1 hour, thetemperature of a semi-sintered body in a mold is not made uniform andwhen the pressing pressure is applied in this state, a problem arises inthat a uniform density distribution and uniform structure cannot beobtained due to an irregular temperature distribution. On the otherhand, when the time exceeds 5 hours, although the temperature of thesemi-sintered body in the mold is completely made uniform, the holdingof the semi-sintered body longer than this time lowers productivity.Thus, the holding time is preferably 2-3 hours.

Further, the pressing pressure is preferably held for 1-8 hours. Whenthe holding time is not longer than 1 hour, many pores remain and a highdensity target cannot be obtained, whereas when it is not shorter than 8hours, since densification does not further proceed, the manufacturingefficiency of a target is lowered. Thus, the holding time is morepreferably 3-5 hours. The sintering for the densification is preferablycarried out in vacuum to prevent the contamination caused by the mixtureof impurities.

An intended sputtering target can be finally obtained by machining aresultant sintered body to a predetermined shape. At that time, it ispreferable to finish the sintered body by a machining method which doesnot produce a surface defect on the surface of the target.

A high purity silicide thin film can be formed by effecting sputteringusing the target. Further, various electrodes such as a gate electrode,source electrode, drain electrode and thin film for a semiconductordevice and a thin film for wiring materials can be formed by subjectingthe thin film to etching and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are electron microphotographs showing the metalstructures of the polished surface and fracture surface of a targetaccording to Example 1, respectively;

FIGS. 2A and 2B are electron microphotographs showing the metalstructures of the polished surface and fracture surface of a targetaccording to Example 6, respectively;

FIGS. 3A and 3B are electron microphotographs showing the metalstructures of the polished surface and fracture surface of a targetaccording to Comparative Example 1, respectively;

FIGS. 4A and 4B are electron microphotographs showing the metalstructures of the polished surface and fracture surface of a targetaccording to Comparative Example 4, respectively;

FIG. 5 is an electron microphotograph showing the metal structure of thesurface of a target semi-sintered body according to Example 11;

FIG. 6 is an electron microphotograph showing the metal structure of thesurface of a target semi-sintered body according to Comparative Example7;

FIG. 7 is an electron microphotograph showing the metal structure of thesurface of a target semi-sintered body according to Comparative Example8;

FIG. 8 is an electron microphotograph showing the metal structure of thesurface of a target semi-sintered body according to Example 12;

FIG. 9 is an electron microphotograph showing the metal structure of thesurface of a target semi-sintered body according to Comparative Example9; and

FIG. 10 is an electron microphotograph showing the metal structure ofthe surface of a target semi-sintered body according to ComparativeExample 10.

BEST MODE FOR CARRYING OUT THE INVENTION

An arrangement and advantage of the present invention will be describedin more detail with reference to the following examples.

EXAMPLES 1-10

A high purity M powder (M: W, Mo shown in Table 1) having a maximumgrain size of 15 μm and a high purity Si powder having a maximum grainsize of 30 μm were prepared and the respective powders were charged intoa ball mill the inside of which was lined with high purity Mo togetherwith high purity Mo balls and then mixed for 48 hours with thereplacement with an Ar gas. Each of the resultant mixed powders wascharged into a high purity Mo vessel with a charging depth set to 3 mmwhen M=Mo (weight to be charged was about 250 g) and to 10 mm when M=W(weight to be charged was about 750 g) and silicide was synthesized insuch a manner that the temperature of the vessel was increased stepwisefrom 950° C. to 1300° C. with a temperature width in each step of 50° C.in a vacuum not higher than 1×10⁻⁴ Torr using a vacuum furnace having aMo heater and Mo insulator with a holding time at each step oftemperature set to 1 hour. The high purity materials used had a puritynot less than 5N (not less than 99.999%).

Next, each of semi-sintered bodies obtained by synthesizing the silicidewas charged into a ball mill the inside of which was lined with highpurity Mo together with high purity Mo balls and then crushed andpulverized for 72 hours with the replacement of the inner atmosphere ofthe ball mill with an Ar gas. The resultant crushed powder was chargedinto a high purity Mo vessel having a diameter of 280 mm and deoxidizedby heating the vessel at 1250° C. for 4 hours in a vacuum not higherthan 10⁻⁴ Torr.

Further, the resultant semi-sintered body (about 280 mm in diameter and40 mm thick) was set to a graphite compacting mold lined with a Ta foil,heated to 1000° C. in a vacuum not higher than 10⁻⁴ Torr and then heatedstepwise up to 1380° C. with a temperature width in each step of 50° C.while applying a pressing pressure of 20 kg/cm² thereto with a holdingtime at each step of temperature set to 1 hour. Then, the semi-sinteredbody was hot pressed by a pressing pressure of 300 kg/cm² appliedthereto in 2 hours after the temperature of the semi-sintered body hadreached 1380° C., so that a sintered body having a diameter of 280 mmand a thickness of 14 mm was prepared.

The resultant sintered body was subjected to grinding, polishing andelectric discharging processes and finished to a target having adiameter of 258 mm and a thickness of 10 mm.

COMPARATIVE EXAMPLES 1-6

As Comparative Examples 1-6, an M powder equal to that used in Examples1-10 was mixed with a Si powder having a maximum grain size of 50 μm andsilicide was synthesized in such a manner that each of the resultantmixed powders was charged into a vacuum vessel having a conventionalcarbon (C) heater and carbon (C) insulator and heated to 1300° C. at arate of 10° C./min in a vacuum not higher than 1×10⁻⁴ Torr with acharging depth set to 6 mm when M=Mo and to 20 mm when M=W.

Next, the crushed powder was charged into in a graphite compacting moldwithout being deoxidized and heated to 1000° C. in vacuum and thenheated up to 1380° C. while applying a pressing pressure of 200 kg/cm²thereto, held for 2 hours and then hot pressed, in the same way as thatof Example 1, so that sintered bodies each having a diameter of 280 mmand a thickness of 14 mm were prepared.

The cross-sectional structures of Example 1-10 and Comparative Examples1-6 were observed under a scanning type electron microscope (SEM) andthe number of MSi₂ independently existing in a cross section of 0.01mm², the average grain size of MSi₂ and the maximum grain size of Siwere measured. Table 1 shows the result of measurement. Further, FIGS.1A, 2A, 3A and 4A show electron microphotographs of the metal structuresof the polished surfaces of target sintered bodies relating to Examples1 and 6 and Comparative Examples 1 and 4, respectively. FIGS. 1B, 2B, 3Band 4B show electron microphotographs of the metal structures of thefracture surfaces of the above target sintered bodies, respectively.Note, the measured values are average values determined by examining across section at 20 positions. Further, a grain size is shown by thediameter of a minimum circle circumscribing a grain.

TABLE 1 AVERAGE NUMBER OF AVERAGE MAXIMUM DISPERSION OF COMPOSITIONINDEPENDENT GRAIN SIZE GRAIN SIZE COMPOSITION SPECIMEN No. OF TARGETMSi₂ (PIECES) OF MSi₂ (μm) OF Si (μm) (Si/M ATOMIC RATIO) EXAMPLE 1WSi_(2.8) 8 8 14 2.80 ± 0.01 EXAMPLE 2 WSi_(2.8) 5 5 15 2.80 ± 0.01EXAMPLE 3 WSi_(2.8) 8 5 11 2.80 ± 0.01 EXAMPLE 4 WSi_(2.8) 10 6 9 2.80 ±0.01 EXAMPLE 5 WSi_(2.8) 14 7 13 2.80 ± 0.01 EXAMPLE 6 MoSi_(2.7) 7 8 142.70 ± 0.01 EXAMPLE 7 MoSi_(2.7) 6 7 9 2.70 ± 0.01 EXAMPLE 8 MoSi_(2.7)8 9 10 2.70 ± 0.01 EXAMPLE 9 MoSi_(2.7) 11 6 11 2.70 ± 0.01 EXAMPLE 10MoSi_(2.7) 14 6 7 2.70 ± 0.01 COMPARATIVE WSi_(2.8) 17 18 35 2.75 ± 0.03EXAMPLE 1 COMPARATIVE WSi_(2.8) 24 21 42 2.74 ± 0.03 EXAMPLE 2COMPARATIVE WSi_(2.8) 30 20 32 2.72 ± 0.04 EXAMPLE 3 COMPARATIVEMoSi_(2.7) 19 22 28 2.63 ± 0.03 EXAMPLE 4 COMPARATIVE MoSi_(2.7) 26 2438 2.61 ± 0.03 EXAMPLE 5 COMPARATIVE MoSi_(2.7) 34 25 42 2.60 ± 0.04EXAMPLE 6

As is apparent from the result shown in Table 1 and FIG. 1-FIG. 4,Examples 1-10 have a fine uniform structure in which MSi₂ grains arelinked or coupled with each other like chain, the less number of MSi₂independently exist, and Si is dispersed in the gaps of the MSi₂ andfurther MSi₂ and Si have a small grain size as compared with ComparativeExamples 1-6. More specifically, it is found that in the metalstructures of the targets of the examples shown in FIGS. 1 and 2, amixed structure is formed such that fine MSi₂ grains shown by grayportions are coupled with each other like a chain and fine Si grainsshown by black portions disperse among them, whereas in the metalstructures of the targets of the comparative examples shown in FIGS. 3and 4, coarse MSi₂ grains (gray portions) and Si grains (black portions)grow as well as a ratio of fine MSi₂ grains independently existing in aSi phase is increased and thus the targets have a structure in whichparticles are liable to be generated.

Table 1 also shows the result of analysis of a Si/W atom ratio in across section of 1 mm² of the mixed structure of each target effected bya surface analyzing instrument (X-ray microanalyzer: EPMA). It is foundfrom the result of analysis that the Examples 1-10 have compositionsnearer to an intended composition as compared with the ComparativeExamples 1-6 and further have uniform compositions.

Table 2 shows the result of measurement of the densities of therespective targets and the result of analysis of oxygen, carbon, ironand aluminium.

TABLE 2 DISPERSION OF NUMBER OF AVERAGE COMPOSITION DENSITY RATIO AMOUNTOF IMPURITY (ppm) PARTICLES SPECIMEN No. OF TARGET (%) O₂ C Fe Al(PIECES) EXAMPLE 1 WSi_(2.8) 99.8 ± 0.1 153 35 0.3 0.2  5 EXAMPLE 2WSi_(2.8) 99.7 ± 0.1 130 28 0.2 0.3 12 EXAMPLE 3 WSi_(2.8) 99.7 ± 0.2186 24 0.4 0.1 19 EXAMPLE 4 WSi_(2.8) 99.8 ± 0.1 120 31 0.5 0.3 25EXAMPLE 5 WSi_(2.8) 99.8 ± 0.1  87 19 0.4 0.3 30 EXAMPLE 6 MoSi_(2.7)99.7 ± 0.2  95 24 0.3 0.1  6 EXAMPLE 7 MoSi_(2.7) 99.7 ± 0.1 122 18 0.20.2 11 EXAMPLE 8 MoSi_(2.7) 99.8 ± 0.1 105 27 0.4 0.4 20 EXAMPLE 9MoSi_(2.7) 99.8 ± 0.1 145 36 0.3 0.2 24 EXAMPLE 10 MoSi_(2.7) 99.7 ± 0.1116 33 0.3 0.1 33 COMPARATIVE EXAMPLE 1 WSi_(2.8) 99.0 ± 0.3 893 128 1.8 1.4 235  COMPARATIVE EXAMPLE 2 WSi_(2.8) 98.8 ± 0.4 952 133  2.3 1.6280  COMPARATIVE EXAMPLE 3 WSi_(2.8) 98.5 ± 0.3 1025  121  2.1 1.2 322 COMPARATIVE EXAMPLE 4 MoSi_(2.7) 99.1 ± 0.3 1230  158  3.4 2.4 256 COMPARATIVE EXAMPLE 5 MoSi_(2.7) 98.8 ± 0.4 1304  168  2.8 2.6 293 COMPARATIVE EXAMPLE 6 MoSi_(2.7) 98.6 ± 0.4 1156  150  3.1 2.1 335 

As apparent from the result shown in Table 2, since the target relatingExamples 1-10 have a density ratio not less than 99.5%, it found thatExamples 1-10 have a very small content of impurities as compared withComparative Examples 1-6.

The respective sputtering targets relating to Examples 1-10 andComparative Examples 1-6 were set to a magnetron sputtering apparatusand sputtered under the condition of an argon pressure of 2.3×10⁻³ Torrand a silicide film was deposited on a 6 inch Si wafer to about 3000 Åthick. The same operation was effected 10 times and an amount of mixedparticles having a particle size not less than 0.2 μm was measured andTable 2 also shows the result of the measurement. As apparent from theresult shown in Table 2, it is found that according to the targetsrelating to Examples 1-10, the number of particles mixed onto the 6 inchwafer is not greater than 33 and very small, whereas according toComparative Examples 1-6, a lot of particles which are about 10 timesthose of Examples 1-10 are generated.

EXAMPLE 11

4658 g of a high purity (5N) W powder having a maximum grain size of 8μm and 1992 g of a high purity (5N) Si powder having a maximum grainsize of 30 μm were prepared, the respective powders were charged into aball mill the inside of which was lined with high purity Mo togetherwith high purity Mo balls and then mixed for 48 hours with thereplacement of the inner atmosphere of the ball mill with an argon gas.The resultant mixed powder having a Si/W atomic ratio of 2.80 wasdivided to each charging depth of 3 mm (weight to be charged was about250 g) and charged into a high purity Mo vessel and silicide wassynthesized in such a manner that the temperature of the vessel wasincreased stepwise from 950° C. to 1300° C. with a temperature width ineach step of 50° C. in a vacuum not higher than 1×10⁻⁴ Torr using avacuum furnace having a Mo heater and Mo insulator with a holding timeat each step of temperature set to 1 hour, so that semi-sintered bodiesof Example 11 were prepared.

COMPARATIVE EXAMPLES 7-8

On the other hand, a semi-sintered body was prepared as ComparativeExample 7 by heating all the amount of the mixed powder for a singlesheet of a target prepared in Example 11 from 950° C. to 1300° C. invacuum at a temperature increasing rate of 10° C./minute. In addition, asemi-sintered body was prepared as Comparative Example 8 by dividing amixed powder similar to that of Example 11 to each charging depth of 3mm and then continuously heating the powder up to 1300° C. at atemperature increasing rate of 10° C./minute in a vacuum not higher than1×10⁻⁴ Torr.

The surface metal structures of respective target semi-sintered bodiesof Example 11, Comparative Examples 7 and 8 were magnified and observedunder a scanning type electron microscope (SEM) and microphotographsshown in FIGS. 5, 6 and 7 were obtained. Then, as the result ofexamination of the maximum grain sizes of WSi₂ grains and Si grainsconstituting the respective metal structures in FIG. 5-FIG. 7, it can beconfirmed that the grain sizes of the respective grains in Example 11are smaller than those of Comparative Examples 7 and 8 and a finestructure is formed and the generation of particles are more lowered inExample 11.

Table 3 shows the result of analysis of the compositions of thesemi-sintered bodies obtained by synthesization. As a result, the degreeof dislocation of the composition of Example 11 is smaller than those ofComparative Examples 7 and 8.

EXAMPLE 12

2850 g of a high purity (5N) Mo powder having a maximum grain size of 5μm and 2250 g of a high purity (5N) Si powder having a maximum grainsize of 30 μm were prepared, the respective powders were charged into aball mill the inside of which was lined with high purity Mo togetherwith high purity Mo balls and then mixed for 48 hours with thereplacement of the inner atmosphere of the ball mill with an Ar gas. Theresultant mixed powder having a Si/W atomic ratio of 2.70 was divided toeach charging depth of 1.5 mm (weight to be charged was about 100 g) andcharged into a high purity Mo vessel, silicide was synthesized in such amanner that the temperature of the vessel was increased stepwise from900° C. to 1250° C. with a temperature width in each step of 50° C. in avacuum not higher than 1×10⁻⁴ Torr using a vacuum furnace having a Moheater and a Mo insulator with a holding time at each step oftemperature set to 1 hour, so that a semi-sintered body of Example 12was prepared.

COMPARATIVE EXAMPLES 9-10

On the other hand, a semi-sintered body was prepared as ComparativeExample 9 by heating all the amount of the mixed powder for a singlesheet of the target prepared in Example 12 from 900° C. to 1250° C. inthe same vacuum at a temperature increasing rate of 10° C./minute. Inaddition, a semi-sintered body was prepared as Comparative Example 10 bydividing a mixed powder equal to that of Example 12 to each chargingdepth of 1.5 mm and then continuously heating the powder up to 1250° C.at a heating rate of 10° C./minute in a vacuum not higher than 1×10⁻⁴Torr.

The surface metal structures of respective target semi-sintered bodiesof Example 12, Comparative Examples 9 and 10 were magnified and observedunder a scanning type electron microscope (SEM) and microphotographsshown in FIGS. 8, 9 and 10 were obtained, respectively. Then, as theresult of measurement of the grain size of MoSi₂ grains (gray portions)and Si grains (black portions) constituting respective metal structuresand analysis of dispersion of the compositions of the respectivesemi-sintered bodies in FIGS. 8-10, the result shown in Table 3 wasobtained.

TABLE 3 AVERAGE DISPERSION OF COMPOSITION SEMI-SINTERED OF SEMI- BODYSPECIMEN No. SINTERED BODY COMPOSITION EXAMPLE 11 WSi_(2.79) 2.79 ± 0.01EXAMPLE 12 MoSi_(2.68) 2.68 ± 0.01 COMPARATIVE WSi_(2.65) 2.65 ± 0.03EXAMPLE 7 COMPARATIVE WSi_(2.69) 2.69 ± 0.04 EXAMPLE 8 COMPARATIVEMoSi_(2.45) 2.45 ± 0.03 EXAMPLE 9 COMPARATIVE MoSi_(2.56) 2.56 ± 0.04EXAMPLE 10

As is apparent from the result shown in Table 3 and FIGS. 8-10, thegrain size of MoSi₂ grains in Example 12 is smaller than that ofComparative Examples 9 and 10 and Example 12 can obtain a fine uniformmetal structure with a small grain size.

Further, as the result of analysis of the compositions of thesemi-sintered bodies obtained by the synthesization, it is found thatExample 12 can provide a target whose composition is less dislocatedthan the targets of Comparative Examples 9 and 12 and which is morehomogeneous than the targets thereof.

Next, a difference of deoxidizing effects will be described.

EXAMPLE 13

The semi-sintered body obtained in Example 11 was charged into a ballmill the inside of which was lined with a high purity Mo materialtogether with high purity Mo balls and crushed for 48 hours with thereplacement of the inner atmosphere of the ball mill with an Ar gas. Theresultant crushed powder was charged into a high purity Mo vessel havinga diameter of 280 mm and the vessel was heated at 1250° C. for 4 hoursin a vacuum not higher than 1×10⁻⁴ Torr.

EXAMPLE 14

On the other hand, a mixed powder equal to that of Example 13 was heatedat 1100° C. for 4 hours in a vacuum not higher than 1×10⁻⁴ Torr asExample 14.

Table 4 shows the result of analysis of oxygen in the respectivesemi-sintered bodies of Example 13 and Example 14.

As is apparent from the result shown in Table 4, it is confirmed that anoxygen content of Example 13 is reduced to about ⅓ that of Example 14.

EXAMPLE 15

The semi-sintered body obtained in Example 12 was charged into a ballmill the inside of which was lined with a high purity Mo materialtogether with high purity Mo balls and crushed for 48 hours with thereplacement of the inner atmosphere of the ball mill with an Ar gas. Theresultant crushed powder was charged into a high purity Mo vessel havinga diameter of 280 mm and the vessel was heated at 1250° C. for 4 hoursin a vacuum not higher than 1×10⁻⁴ Torr.

EXAMPLE 16

On the other hand, a mixed powder equal to that of Example 15 was heatedat 1100° C. for 4 hours in a vacuum not higher than 1×10⁻⁴ Torr asExample 16.

Table 4 shows the result of analysis of oxygen content in the respectivesemi-sintered bodies of Example 15 and Example 16.

EXAMPLE 17

The semi-sintered body obtained in Example 11 was charged into a ballmill the inside of which was lined with a Mo high purity materialtogether with high purity Mo balls and crushed for 48 hours with thereplacement of the inner atmosphere of the ball mill with an Ar gas. Theresultant crushed powder was charged into a high purity Mo vessel havinga diameter of 280 mm, the vessel was evacuated to 1×10⁻⁴ Torr andhydrogen was introduced into the vessel and then the vessel was heatedat 1250° C. for 4 hours in an atmosphere reduced to 0.1 Torr. Table 4shows the result of analysis of the oxygen content of the resultantspecimens (semi-sintered bodies).

TABLE 4 AMOUNT OF OXYGEN SPECIMEN No. (ppm) EXAMPLE 13 110 EXAMPLE 14380 EXAMPLE 15 140 EXAMPLE 16 140 EXAMPLE 17 85

As is apparent from the result shown in Table 4, according to Example15, the oxygen content of the semi-sintered body is reduced to about ⅓that of Example 16.

Further, as shown in Example 17, a higher deoxidizing effect can beobtained when impurities are removed in a reduced pressure atmospherewith hydrogen introduced thereinto rather than when they are removed ina simple vacuum atmosphere.

As described above, the semi-sintered bodies of the refractory metalsilicide obtained by the manufacturing method of the examples can easilyprovide a target with a low oxygen content because the semi-sinteredbodies contain a very small amount of oxygen. As a result, theemployment of the target can reduce a film resistance and improve thereliability of semiconductor devices.

EXAMPLES 18-23

A high purity W powder or high purity Mo powder each having a maximumgrain size of 15 μm was mixed with a high purity Si powder having amaximum grain size of 30 μm, and silicide was synthesized by heating theresultant mixed powder in vacuum. Further, many semi-sintered bodies of280 mm in diameter and 40 mm thick having an average composition ofWSi_(2.8) or MoSi_(2.7) were prepared in such a manner that asemi-sintered body obtained by synthesizing the silicide was crushed ina ball mill and the resultant crushed powder was deoxidized by beingheated in vacuum.

Next, silicide targets relating to Examples 18-23, respectively weremade by subjecting the resultant semi-sintered bodies obtained to hotpressing under a pressing condition and heating condition each composedof two steps shown in Table 5. Note, the heating condition was such thatthe semi-sintered bodies were continuously heated up to 1000° C. at atemperature increasing rate of 5-20° C./minute and then heated stepwisefrom 1000° C. to 1380° C. with a temperature width in each step of50-150° C.

COMPARATIVE EXAMPLES 11-15

On the other hand, the semi-sintered bodies used in Examples 19-23 werehot pressed under a pressing condition and heating conditions eachcomposed of two steps, and silicide targets relating to ComparativeExamples 11-15 were made.

The mixed structures of the resultant silicide targets relating toExamples 18-23 and Comparative Examples 11-15 were observed under ascanning type electron microscope and the average grain size of WSi₂grains and MoSi₂ grains and the maximum grain size of Si grainsconstituting the mixed structures were measured and the compositions ofthe respective silicide targets were analyzed at the center portions andend portions thereof. Table 5 shows the result of the measurement andanalysis.

TABLE 5 AVERAGE COMPOSITION PRESSURIZING HEATING CONDITIONS GRAINMAXIMUM OF TARGET AVERAGE CONDITIONS HOLDING SIZE OF GRAIN (Si/M ATOMICRATIO) SPECIMEN COMPOSITION 1st STEP 2nd STEP TEMPERATURE PERIOD MSi₂SIZE OF Si END CENTER No. OF TARGET (kg/cm²) (kg/cm²) WIDTH (° C.) OFTIME (hr) (μm) (μm) PORTION PORTION EXAMPLE 18 WSi_(2.8) 20 300  50 1 8 8 2.78 2.79 EXAMPLE 19 WSi_(2.8) 30 300 100 2 7 10 2.79 2.79 EXAMPLE 20WSi_(2.8) 40 300 150 3 5 14 2.79 2.79 EXAMPLE 21 MoSi_(2.7) 10 300  50 17  7 2.68 2.69 EXAMPLE 22 MoSi_(2.7) 20 300 100 2 6 10 2.69 2.69 EXAMPLE23 MoSi_(2.7) 30 300 150 3 5 14 2.69 2.69 COMPAR- WSi_(2.8) 250  300 1002 6 25 2.79 2.79 ATIVE EXAMPLE 11 COMPAR- WSi_(2.8) 30 300 400 1 12  122.77 2.80 ATIVE EXAMPLE 12 COMPAR- MoSi_(2.7) 150  300  50 1 6 22 2.682.69 ATIVE EXAMPLE 13 COMPAR- MoSi_(2.7) 200  300 100 2 8 27 2.68 2.69ATIVE EXAMPLE 14 COMPAR- MoSi_(2.7)  0 300 400 1 15  15 2.65 2.69 ATIVEEXAMPLE 15

In the targets relating to Examples 18-23, since Si plastically flows,disperses and moves to the gaps of the semi-sintered bodies and fillsthe gaps under the condition of a low pressing pressure, a less amountof Si is segregated and uniformly dispersed. Thus, as apparent from theresult shown in Table 5, the WSi₂ grains, MoSi₂ grains and Si grains ofthe targets of the respective examples have grain sizes smaller thanthose of the comparative examples, so that fine and miniaturized mixedstructures are obtained. Further, it is found that the composition (Si/Matomic ratio) of each of the targets of the examples is less dispersedat the center and end portion thereof and exhibits a composition moreuniformly distributed than that of the comparative examples.

On the other hand, it is found that when a high pressure is applied fromthe initial stage of the start of sintering as in the targets ofComparative Examples 11, 13, 14, since a Si component is restricted andplastic flowing is difficult to occur, Si grains are coarsened and afine mixed structure cannot be obtained.

Further, it is also found that when targets are abruptly heated under alow pressing pressure as in the targets of Comparative Examples 12 and15, MSi₂ grains grow and a fine structure cannot be obtained likewise.

EXAMPLES 24-34

A high purity M (M: W, Mo, Ti, Zr, Hf, Nb, Ta, V, Co, Cr, Ni shown inTable 6) powder having a maximum grain size of 15 μm and a high puritySi powder having a maximum grain size of 30 μm were prepared and therespective powders were charged into a ball mill the inside of which waslined with high purity Mo together with high purity Mo balls and mixedfor 48 hours with the replacement of the inner atmosphere of the ballmill with an Ar gas. The resultant respective mixed powders were chargedinto a high purity Mo vessel. The depth and weight of the mixed powdersto be charged were set to 5 mm and about 2000 g, respectively. Thevessel was then heated stepwise in the temperature range from 800° C. to1300° C. (different depending upon a material) in a vacuum not higherthan 1×10⁻⁴ Torr with a temperature width in each step of 50° C. with aholding time at each step temperature set to 1 hour, so that silicidewas synthesized. High purity materials not less than 5N were used as therespective high purity materials.

Next, semi-sintered bodies obtained by synthesizing the suicide werecharged into a ball mill the inside of which was lined with high purityMo together with high purity Mo balls and then mixed for 48 hours withthe replacement of the inner atmosphere of the ball mill with an Ar gas.The resultant crushed powders were charged into a high purity Mo vesselhaving a diameter of 280 mm and the vessel was heated at 1250° C. for 4hours in a vacuum not higher than 1×10⁻⁴ Torr to subject the powders toa deoxidizing treatment.

Further, resultant semi-sintered bodies (about 280 mm in diameter×40 mmthick) were set to a graphite compacting mold the inside of which waslined with a Ta foil and heated to 1000° C. in a vacuum not higher than1×10⁻⁴ Torr. Then, the temperature of the semi-sintered bodies wasincreased stepwise up to a temperature 30° C. lower than the eutectictemperature of each material (final temperature) with a temperaturewidth in each step of 50° C. with a holding time of each temperature setto 1 hour while applying a low pressing pressure of 20 kg/cm² to thesemi-sintered bodies. Then, the semi-sintered bodies were hot pressedwith a high pressing pressure of 350 kg/cm² in 2 hours after the finaltemperature was reached, so that sintered bodies each having a diameterof 280 mm and a thickness of 14 mm were made.

The resultant sintered bodies were subjected to grinding, polishing andelectric discharging processes and finished to targets each having adiameter of 258 mm and a thickness of 10 mm.

COMPARATIVE EXAMPLES 16-26

As Comparative Examples 16-26, an M powder similar to that of Examples24-34 was mixed with a Si powder having a maximum grain size of 50 μmand the resultant respective powders were charged into a vacuum furnacehaving a conventional carbon (C) heater and carbon (C) insulator with acharging depth set to 20 mm and heated to the temperature range from 800to 1300° C. (different depending upon a material) at a rate of 10°C./minute in a vacuum not higher than 1×10⁻⁴ Torr and semi-sinteredbodies were obtained by synthesizing silicide.

Next, the semi-sintered bodies obtained by synthesizing the silicidewere set to a graphite compacting mold without being deoxidized andheated to 1000° C. in vacuum. Then, the temperature of the semi-sinteredbodies was increased up to a temperature 30° C. lower than the eutectictemperature of each material (final temperature) while applying apressing pressure of 200 kg/cm² to the semi-sintered bodies. Then, thesemi-sintered bodies were held for 2 hours to be hot pressed, so thatsintered bodies each having a diameter of 280 mm and a thickness of 14mm were made and further finished to targets having the same dimensionas that of the above examples.

The cross-sectional structures of the respective targets relating toExample 24-34 and Comparative Examples 16-26 were observed under ascanning type electron microscope (SEM) and the number of MSi₂independently existing in a cross section of 0.01 mm², the average grainsize of MSi₂ and the maximum grain size of Si were measured. Table 6shows the result of the measurement. Note, the measured values areaverage values determined by examining a cross section at 20 positions.Further, a grain size is shown by the diameter of a minimum circlecircumscribing a grain.

TABLE 6 (To be continued) AVERAGE NUMBER OF AVERAGE MAXIMUM DISPERSIONOF COMPOSITION INDEPENDENT GRAIN SIZE GRAIN SIZE COMPOSITION SPECIMENNo. OF TARGET MSi₂ (PIECES) OF MSi₂ (μm) OF Si (μm) (Si/M ATOMIC RATIO)EXAMPLE 24 WSi_(2.8) 9 7 15 2.80 ± 0.01 EXAMPLE 25 MoSi_(2.7) 10 9 132.70 ± 0.01 EXAMPLE 26 TiSi_(2.7) 6 7 15 2.70 ± 0.01 EXAMPLE 27ZrSi_(2.6) 12 9 12 2.60 ± 0.01 EXAMPLE 28 HfSi_(2.5) 10 7 10 2.50 ± 0.01EXAMPLE 29 NbSi_(2.7) 8 5 11 2.70 ± 0.01 EXAMPLE 30 TaSi_(2.6) 6 8 92.60 ± 0.01 EXAMVLE 31 VSi_(2.5) 9 7 13 2.50 ± 0.01 EXAMPLE 32CoSi_(2.6) 11 9 12 2.60 ± 0.01 EXAMPLE 33 CrSi_(2.7) 7 7 10 2.70 ± 0.01EXAMPLE 34 NiSi_(2.7) 12 9 13 2.70 ± 0.01

TABLE 6 AVERAGE NUMBER OF AVERAGE MAXIMUM DISPERSION OF COMPOSITIONINDEPENDENT GRAIN SIZE GRAIN SIZE COMPOSITION SPECIMEN No. OF TARGETMSi₂ (PIECES) OF MSi₂ (μm) OF Si (μm) (Si/M ATOMIC RATIO) COMPARATIVEWSi_(2.8) 21 20 29 2.74 ± 0.03 EXAMPLE 16 COMPARATIVE MoSi_(2.7) 23 2130 2.64 ± 0.03 EXAMPLE 17 COMPARATIVE TiSi_(2.7) 25 26 32 2.73 ± 0.03EXAMPLE 18 COMPARATIVE ZrSi_(2.6) 20 21 27 2.55 ± 0.03 EXAMPLE 19COMPARATIVE HfSi_(2.5) 33 24 28 2.43 ± 0.03 EXAMPLE 20 COMPARATIVENbSi_(2.7) 27 21 34 2.64 ± 0.03 EXAMPLE 21 COMPARATIVE TaSi_(2.6) 25 2822 2.54 ± 0.04 EXAMPLE 22 COMPARATIVE VSi_(2.5) 23 19 30 2.44 ± 0.03EXAMPLE 23 COMPARATIVE CoSi_(2.6) 29 22 32 2.55 ± 0.03 EXAMPLE 24COMPARATIVE CrSi_(2.7) 27 24 29 2.65 ± 0.04 EXAMPLE 25 COMPARATIVENiSi_(2.7) 25 26 21 2.65 ± 0.03 EXAMPLE 26

As apparent from the result shown in Table 6, Examples 24-34 have auniform and fine structure in which the less number of MSi₂independently exist and Si disperses in the gaps of the MSi₂, andfurther MSi₂ and Si have a small grain size as compared with ComparativeExamples 16-26. Further, in each of the targets of the respectiveexamples, a mixed structure is formed such that fine MSi₂ grains shownby white portions are coupled with each other like a chain and fine Sigrains shown by black portions disperse among them similarly to themetal structures of the targets of Examples 1 and 6 shown in FIGS. 1 and2. On the other hand, it is found that in the targets relating toComparative Examples 16-26, coarse MSi₂ grains (gray portions) and Sigrains (black portions) grow as well as a ratio of fine MSi₂ grainsindependently existing in a Si phase is increased and thus the targetshave a structure in which particles are liable to be generated similarlyto the metal structures of the targets relating to Comparative Examples1 and 4 shown in FIGS. 3 and 4.

Table 6 also shows the result of analysis of a Si/W atomic ratio in across section of 1 mm² of the mixed structure of each target obtained bya surface analyzing instrument (X-ray microanalyzer: EPMA). It is foundfrom the result of analysis that the examples have compositions nearerto an intended composition as compared with the comparative examples andfurther have uniform compositions.

Table 7 shows the result of measurement of the densities of therespective targets and the result of analysis of oxygen, carbon, ironand aluminium.

TABLE 7 AVERAGE NUMBER OF COMPOSITION DISPERSION OF AMOUNT OF IMPURITY(ppm) PARTICLES SPECIMEN No. OF TARGET DENSITY RATIO O₂ C Fe Al (PIECES)EXAMPLE 24 WSi_(2.8) 99.8 ± 0.1 135  30 0.4 0.1  8 EXAMPLE 25 MoSi_(2.7)99.8 ± 0.1 141  25 0.5 0.3  9 EXAMPLE 26 TiSi_(2.7) 99.7 ± 0.1 185  330.6 0.2  15 EXAMPLE 27 ZrSi_(2.6) 99.8 ± 0.1 122  30 0.5 0.3  16 EXAMPLE28 HfSi_(2.5) 99.8 ± 0.1 179  34 0.7 0.3  13 EXAMPLE 29 NbSi_(2.7) 99.8± 0.1 165  25 0.5 0.2  17 EXAMPLE 30 TaSi_(2.6) 99.7 ± 0.2 143  37 0.60.3  9 EXAMPLE 31 VSi_(2.5) 99.7 ± 0.1 178  35 0.7 0.3  17 EXAMPLE 32CoSi_(2.6) 99.8 ± 0.1 188  38 0.6 0.2  18 EXAMPLE 33 CrSi_(2.7) 99.7 ±0.1 155  31 0.8 0.4  14 EXAMPLE 34 NiSi_(2.7) 99.7 ± 0.2 187  40 0.8 0.3 20 COMPARATIVE EXAMPLE 16 WSi_(2.8) 99.1 ± 0.3 954 117 2.1 2.2 257COMPARATIVE EXAMPLE 17 MoSi_(2.7) 99.0 ± 0.3 1180  123 3.1 2.3 277COMPARATIVE EXAMPLE 18 TiSi_(2.7) 98.5 ± 0.4 3475  188 4.5 3.3 327COMPARATIVE EXAMPLE 19 ZrSi_(2.6) 98.6 ± 0.3 1946  170 3.8 2.2 244COMPARATIVE EXAMPLE 20 HfSi_(2.5) 98.8 ± 0.3 1737  152 3.2 3.1 217COMPARATIVE EXAMPLE 21 NbSi_(2.7) 98.7 ± 0.4 2254  162 4.0 2.9 289COMPARATIVE EXAMPLE 22 TaSi_(2.6) 98.5 ± 0.4 2790  189 4.2 3.1 336COMPARATIVE EXAMPLE 23 VSi_(2.5) 98.6 ± 0.3 2774  175 3.9 2.7 297COMPARATIVE EXAMPLE 24 CoSi_(2.6) 99.0 ± 0.3 1995  147 3.5 2.5 207COMPARATIVE EXAMPLE 25 CrSi_(2.7) 98.7 ± 0.3 2065  155 3.7 2.6 268COMPARATIVE EXAMPLE 26 NiSi_(2.7) 98.4 ± 0.4 3358  189 4.5 3.9 357

As is apparent from the result shown in Table 7, it was found that thetargets relating to Examples 24-34 have a density ratio not less than99.5% and a very small content of impurities as compared with thetargets relating to Comparative Examples 16-26.

The respective targets relating to Examples 24-34 and ComparativeExamples 16-26 were set to a magnetron sputtering apparatus andsputtered under the condition of an argon pressure of 2.3×10⁻³ Torr anda silicide film was deposited on a 6 inch Si wafer to about 3000Å thick.The same operation was repeated 10 times and an amount of mixedparticles having a particle size not less than 0.2 μm was measured.Table 7 also shows the result of the measurement. As also apparent fromthe result shown in Table 7, according to the targets relating toExamples 24-34, the number of particles mixed on the 6 inch wafer is notgreater than 20 and very small, whereas according to ComparativeExamples 16-26, it is found that a lot of particles which are about 10times those of Examples 24-34 are generated.

Industrial Applicability:

As described above, the refractory metal silicide targets according tothe present invention have a high purity, high density fine mixedstructure composed of refractory metal silicide grains and Si grains inwhich Si grains uniformly disperse and, the compositions in the targetsare uniformly arranged. Consequently, the employment of the targetsreduces particles produced in sputtering, the change of a filmresistance on a wafer surface and the impurities and the like in thefilm of the wafer face and can improve yield and reliability whensemiconductors are manufactured.

What is claimed is:
 1. A refractory metal silicide target, comprising afine mixed structure composed of MSi₂ grains, wherein M is at least onerefractory metal selected from W, Mo, Ti, Ta, Zr, Hf, Nb, V, Co, Cr, Ni;and Si grains, wherein the number of MSi₂ grains independently existingin a cross section of 0.01 mm² of the mixed structure is not greaterthan 15, the MSi₂ grains have an average grain size not greater than 10μm, whereas free Si grains existing in gaps of the MSi₂ grains have amaximum grain size not greater than 20 μm.
 2. A refractory metalsilicide target according to claim 1, wherein when the average value ofa Si/M atomic ratio in the entire sputtering target is assumed to be X,the dispersion of the Si/M atomic ratio in an arbitrary cross section of1 mm² in the mixed structure is in a range of X±0.02.
 3. A refractorymetal silicide target according to claim 1, wherein a density ratio isnot less than 99.5% over the entire target.
 4. A refractory metalsilicide target according to claim 1, wherein an oxygen content is notgreater than 200 ppm and a carbon content is not greater than 50 ppm. 5.A refractory metal silicide target according to claim 1, wherein an ironcontent and an aluminium content are not greater than 1 ppm,respectively.